This invention relates to the measurement of Doppler frequency and, more particularly, to the modification of the Doppler power spectrum for extraction of Doppler data therefrom.
The measurement of Doppler frequency is often accomplished by one or more filters which signal the magnitude of the frequency, or by means of timing circuits which provide the time elapsed by a specified number of cycles of the Doppler signal. Such systems are intended for use primarily in a situation providing clear unambiguous Doppler signals.
A problem arises in the case of reverberant and nonlinear radiation transmissive media, such as the ocean which is transmissive of radiant sonic energy, in that such a medium with its multifarious reflecting boundaries, such as mud and rock, alters a Doppler signal. The altered signal is characterized by a broadened spectrum which is inherently ambiguous to Doppler frequency measurement, the spectrum providing many possible values of Doppler frequency which derogate from an accurate measurement of the Doppler frequency.